heart rate monitor is not accurate and often doesn't work at all

[jjb149]

The heart rate meter works only sometimes now.  It often doesn't show any heart rate.  I'm always having to reset it.  It's also completely useless for tracking heart rate during high intensity interval training (HIIT) because it can't keep up with the large changes it heart rate over short amounts of time (or it shows no heart rate at all).  I'm not wearing it incorrectly and I keep it charged.

With the calorie burn also being so inaccurate, this device seems more like an interesting toy than a useful fitness tracker.

[phatbitzr]

the fitbit displays heartrate based on a moving average, which seems to utilize a longer sample window than my suunto watch that utilizes a chest strap.  Thus when it have problem sampling heartrate, instead of showing the new HR, it slowly changes to that averaged rate.  It should be smart enough to know that there are beats are so irregular and try to discard samples where the period between beats are way off the prior samples and gather the samples within its window that it consider good.

On the Suunto, the most frequent thing that happens is if the signal is weak, it displays once in a while, 50% of my HR, and once in a blue moon, 33%.  If it picks up 70% of the beats, it won't display my HR as 70% of my actual HR, but knows when the signal is irregular and discards the irregular ones.

[TheCyberKnight]

I've been stuck with a similar issue since the last firmware (version 402 in Fall 2017).

My Blaze was replaced under warranty since and the new one has the exact same issue.

All of this was working fine before, never failing to track my elevated HR.

The reply from @phatbitzr could make sense but I don't think it's the case especially because it was working fine and because, during most of my training sessions, the Blaze is able to track my elevated HR but only for a short amount of time (let's says 10 minutes on a 60 minutes training - and right in the middle of the session).